Parasympathetic activity during parabolic flight, effect of LBNP during microgravity

Area of Science:

• Space physiology
• Autonomic nervous system function
• Cardiovascular regulation

Background:

• Fluid shifts occur in the standing position during parabolic flight due to altered gravity.
• These fluid shifts impact hydrostatic pressure gradients between body segments.
• Changes in parasympathetic activity may be linked to these gravity-induced hydrostatic pressure variations.

Purpose of the Study:

• To investigate if parasympathetic activity modifications can be detected via short-term heart rate variability (HRV) analysis during altered gravity.
• To assess the effect of lower body negative pressure (LBNP) on parasympathetic activity during microgravity.

Main Methods:

• Heart rate variability (HRV) was assessed in 11 healthy volunteers using temporal analysis indices (NN, SDNN, RMSSD) and normalized indices (CV-SDNN, CV-RMSSD, SDNN/RMSSD).
• Lower body negative pressure (LBNP) at -50 mm Hg was applied during the microgravity phase (0 Gz) to simulate hydrostatic pressure.
• Data were collected during hypergravity, microgravity, and normogravity phases of parabolic flight.

Main Results:

• Temporal HRV indices (NN, CV-SDNN, CV-RMSSD) showed decreased values during hypergravity and increased values during microgravity and early post-parabolic normogravity.
• The application of LBNP during microgravity attenuated the observed changes in HRV indices.
• LBNP reduced parasympathetic activation during the 0 Gz phase and the subsequent 1 Gz period.

Conclusions:

• Parasympathetic nervous activity can be reliably recorded using temporal HRV analysis even during short-duration altered gravity exposure.
• Lower body negative pressure (LBNP) effectively mitigates parasympathetic activation during microgravity and the recovery phase.
• HRV analysis provides a sensitive tool for studying autonomic responses to transient changes in gravitational loading.